Original Article

Effect of La₂O₃ and Fe_xO on the viscosity and structure of CaO–MgO–Al₂O₃–SiO₂ melts

¹ Collaborative Innovation Center of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China
² School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China
³ National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China

^* e-mail: anzhuoqing@163.com

Received: 27 January 2024
Accepted: 19 April 2024

Abstract

The effect of La₂O₃ and Fe_xO on the viscosity and structure of CaO–MgO–Al₂O₃–SiO₂ (CMAS) melt was investigated. The viscosity of CaO–MgO–Al₂O₃–SiO₂ melts with La₂O₃ and Fe_xO was measured by a rotating cylindrical method from 1375 °C to 1550 °C, and the structures of the melts were analyzed via Raman spectroscopy. The results indicated that the viscosity decreased with increasing temperature and the activation energy decreased from 111.53 to 99.25 kJ/mol with the mole ratio of La₂O₃/Fe_xO decreased from 2/0 to 0/2. The structural analysis revealed that the weaker chemical bonds or non-chemical bonds between the network structures of the glass were broken with the temperature increases, and both La₂O₃ and Fe_xO acted as network modifiers to simplify the Si–O–Si tetrahedral structural unit. When the mole ratio of La₂O₃/Fe_xO decreased from 2:0 to 0:2, the relative fraction of Q_Si³ and Q_Si⁴ decreased and the relative fraction of Q_Si⁰, Q_Si¹ and Q_Si² increased. Therefore, the degree of polymerization (DOP) of CMAS melt decreased, as well as the viscosity decreased with the addition of Fe_xO and La₂O₃. Fe_xO has more effective on the decrement in CMAS melt viscosity than that of La₂O₃ due to the structure modification ability of La³⁺ being smaller than that of Fe²⁺. Moreover, the number of non-bridging oxygen atoms per tetrahedrally coordinated atom (NBO/T) was used to characterize the melt structure, the quantitative relationship among the viscosity, temperature and microstructure of the melt was given.